By Jessica Hoover, Agricultural and Natural Resources Agent, Associate Professor
Drought damaged crops not only result in decreased yields, but also present new risks for producers. One of the biggest risks of drought damaged crops is increased nitrate levels. Under normal conditions, nitrate uptake is a normal process essential in plant growth. However, under drought conditions, photosynthesis slows, which slows the transportation of nitrates to plant leaves for use, which causes an accumulation of nitrates in the lower portion of the stalks and stems of plants. This is further amplified if nitrogen availability is high, such as fields that received a heavy nitrogen fertilizer. Additionally, receiving rain will cause the nitrate level to spike as the new water availability will increase nitrate uptake. As a result, producers are encouraged to wait to harvest when nitrate levels have returned to normal, if possible, especially following a rain.
High nitrate levels in corn and hay present many challenges for producers. Ruminants are susceptible to nitrate poisoning if elevated levels of nitrates are consumed. This is because nitrate is typically converted to nitrite and used during the protein conversion process, however, at elevated levels, nitrite is unable to be completely used. The excess nitrites then enter the bloodstream and bind to red blood cells, converting hemoglobin to methemoglobin. With hemoglobin in this form, the cells are unable to transport oxygen. At elevated levels of methemoglobin concentration, sudden death of the animal occurs due to oxygen starvation. Other symptoms of nitrate poisoning include weakness; rapid breathing; rapid heartrate; staggering; muscle tremors; brownish discoloration of mucous membranes, blood, or other tissues; and abortions.
When harvesting drought damaged crops, testing is the most valuable tool producers can use to understand not only the nitrate level in the crop, but the nutritional value of the crop. Reductions in yield or grain content may present differing levels of crude protein, fiber, or other nutrients. Raising the cutter bar may result in a reduction in nitrates as most are concentrated in the lower portion of the plant. Ensiling corn for at least 30 days will also reduce the level of nitrates by a third to a half through the fermentation process, however testing is still important both during chopping, and after ensilage to fully understand the nitrate level and nutritional composition of the feed. Nitrate testing is especially important in hay, as nitrate reduction does not occur during the drying process. The only way to know the nitrate level or nutritional value of any feed with certainty is through testing.
According to the University of Kentucky, safe levels of nitrate are below 5,000 ppm or 0.5 percent of dry matter. If levels are above this, up to 10,000 ppm or 1 percent, dilution with other feeds and slow introduction may be acceptable. Levels above 10,000 ppm or 1 percent are considered unsafe and should not be fed.
The Potomac Valley Conservation District offers a cost share program for nitrate, mycotoxin, and mold testing for forages. More information on this program can be obtained from the Potomac Valley Conservation District office. Additionally, the Pendleton County Extension Service is available to aid producers in navigating management of drought damaged crops.
